1. Field of the Invention
The present invention relates to a constantcurrent source circuit which can generate a current output having any desired temperature characteristics and to a differential amplifier which uses the above constant-current source circuit so as to ensure a stable temperature characteristic of, for example, the potentials of its logic output signals.
2. Description of the Prior Art
A constant-current source circuit can generate a current relatively stable against variations of power supply voltage, but not that stable against variations in the ambient temperature.
A constant-current source circuit is typically used in an emitter-coupled-logic (ECL) circuit. Even a slight change in the current of the constant-current source circuit will result in a change in the logic level voltages of the output signal of the ECL circuit, especially when many ECL circuits are coupled in cascade, thereby reducing the voltage margin of the ECL circuit.
To overcome this problem, in a conventional constant current source circuit used in an ECL circuit, the temperature characteristic of the output current is compensated for by using the temperature characteristic of the forward-biased voltage of a diode or of the base-emitter voltage of a bipolar transistor. In another constant current circuit using metal oxide semiconductor (MOS) transistors, the output current is stabilized by using a negative feedback circuit.
In these conventional constant current source circuits, however, it has still been impossible to make the temperature coefficient of the output current completely zero or any desired value.